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Code PO300

Tiny
AMY DEAN
  • MEMBER
  • 2006 SATURN VUE
  • 2.2L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 133,850 MILES
Truck started throwing code po300 misfire. So we started small with MAF sensor, then two o2 sensors, then spark plus and still throwing po300 code. But here is where it gets interesting. We ran it after all that was changed for three days no problem took it for oil change left parking lot and it went right back to the same code and has lack of speed. Spits and sputters and will not go faster than thirty mph with foot to the floor. There was a moment or two where she seems to get a boot in her butt and picks up speed then back to no power. We are getting frustrated. Some help please.
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Saturday, June 2nd, 2018 AT 7:23 PM

4 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,627 POSTS
P0300 - Random multiple misfire. So it is something that can cause a lean or rich condition that is enough to cause cylinders to misfire.
A vacuum leak can do that, so can low fuel pressure. Low fuel pressure will also cause a severe loss of power.
I would start by measuring the fuel pressure, you should have between 50 and 60 psi with the key on engine off. When you turn the key off it should hold that pressure for a while (ideally it will hold forever without any leakage, but they all leak a bit).
Also, look for a broken or cracked vacuum line, these can be hidden in places like the brake booster or even in the EVAP lines.
The easiest way to determine if it is a vacuum leak is to look at the fuel trims with a scan tool and see what they do as you raise the rpm's.
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Saturday, June 2nd, 2018 AT 8:59 PM
Tiny
AMY DEAN
  • MEMBER
  • 3 POSTS
Steve, thank you for the fast response. Will the low fuel pressure cause the truck to run good for a few days and then out of the blue act up again with the loss of power and spitting and sputtering? I just do not get it. We will try the fuel pressure test tomorrow morning. Could it be the injectors or the ignition coil? We were told it could be those as well. We already put over $280.00 in the truck in the last three days. I know there is no quick fix and people say to take it to the shop but I just feel it is something simple. Just at a loss right now. Thanks
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Saturday, June 2nd, 2018 AT 9:10 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,627 POSTS
It could depending on what is causing the problem. A bad connection or failing pump can act this way. Intermittent issues can be hard to track because you need to run the tests while it is acting up. I would start with testing the fuel pressure while it is running bad. Plus looking for any vacuum leaks.
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Sunday, June 3rd, 2018 AT 6:57 AM
Tiny
AMY DEAN
  • MEMBER
  • 3 POSTS
Thank you, we will do this. Keep you posted.
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Sunday, June 3rd, 2018 AT 6:59 AM

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